This invention relates to switching between multiple radio frequency circuits, such as filters.
Selecting one circuit such as a filter, from among a number of such circuits represents a problem at radio frequencies. One of the prior art approaches has been to employ a rotary switch. The switching speed is relatively slow, because the switch must pass through all intermediate positions between an old and a new position. Moreover, the filters or other circuits must be clustered about the rotary switch in order to minimize lead lengths. This leads to packaging restrictions. The inductance in switch and wire leads to the filter inputs are difficult to control in production. Further, radiation from the switch assembly may affect other circuits. Some of these shortcomings may be alleviated by using a coaxial switch; however, these switches are expensive.
Relays have also been used in the past. These also suffer from problems with stray inductance in lead wires and radio frequency coupling to nonselected filters through interconnecting leads. Again, these problems can be alleviated by using coaxial equipment which is expensive. Further, if higher radio frequency power levels, such as one kilowatt, are required, then expensive relays are demanded in order to carry the high current.
In accordance with the present invention, there is provided an apparatus for selecting between multiple radio frequency circuits, which is fast, economical, reliable, has low loss and provides little disruption to the electrical characteristics of the circuits.